Repeater嵌套与判断'checkbox'是否选中

<asp:Repeater ID="Repeater1" runat="server">
<ItemTemplate>
  <table cellspacing="1" cellpadding="0" width="606" align="center"
            bgcolor="#FBCC93" border="0">
    <tbody>
      <tr bgcolor="#ffffff">
        <td height="26" colspan="5" align="center" valign="middle" bgcolor="#E4F6E0" class="lv141"><%#Eval("title") %></td>
      </tr>
     
      <tr bgcolor="#ffffff">
        <td width="177" height="23" align="center" valign="middle" bgcolor="#F4A53C" class="Blue12">
            <span class="bs14">科目名称</span><a href="#" target="_blank"><br />
                </a></td>
        <td width="127" height="23" align="center" valign="middle" bgcolor="#F4A53C" class="bs14">价格</td>
        <td width="112" align="center" valign="middle" bgcolor="#F4A53C" class="bs14">课时</td>
        <td width="71" align="center" valign="middle" bgcolor="#F4A53C" class="bs14">试听</td>
        <td width="113" align="center" valign="middle" bgcolor="#F4A53C" class="bs14">报名</td>
      </tr>
<asp:Repeater ID="Repeater11" runat="server" DataSource=<%# PB.Business.olclass.GetCoursesList((int)Eval("id"), -1) %>>
<ItemTemplate>
<tr bgcolor="#ffffff">
<td height="5" align="center" valign="middle" class="Blue12"><%# Eval("title")%></td>
<td height="5" align="center" valign="middle" class="hui12"><%# Eval("price")%></td>
<td align="center" valign="middle" class="hui12"><%# Eval("courses")%></td>
<td align="center" valign="middle" class="Blue12"><a href="/olclass/keshixuanze.aspx?courseid=<%# Eval("id")%>&isfree=1" target="_blank"><img src="/static/v2/images/jin_but.gif" width="14" height="11" alt=""/></a></td>
<td align="center" valign="middle" class="Blue12"><asp:CheckBox ID="CheckBox1" runat="server" ToolTip='<%# Eval("id")%>' onclick="IsChecked(this);" />
</td>
</tr>
</ItemTemplate>
</asp:Repeater>
 </tbody>
  </table>
  </ItemTemplate>
  </asp:Repeater>

//检测是否选中
    function IsChecked(inst) {
        var num = 0;
        var id = [];
        var idsum = "";
        var items = document.getElementById("xx").getElementsByTagName("input");
        for (var i = 0; i < items.length; i++) {
            if (items[i].type == 'checkbox') {
                if (items[i].checked) {
                    id[i] = parseInt(items[i].parentNode.title);
                    idsum += items[i].parentNode.title + ",";
                    num++;
                }
            }
        }
        if (num == 0) {
            inst.href = "/olclass/onlinebuy.aspx";
            alert("请您选择你要报名的科目");
        }
        else {
            inst.href = "/olclass/buy.aspx?id=" + idsum;
        }
    }